fix: resolve absolute stack frame paths in the webpack compiler

.changeset/webpack-symbolicate-absolute-paths.md

@@ -0,0 +1,5 @@
+---
+"@callstack/repack": patch
+---
+
+Fix the webpack compiler double-joining absolute paths in `getSource`. The dev server resolves symbolicated stack frames to absolute paths before asking the compiler for their source, but the webpack compiler joined them onto the project root a second time, so the lookup failed. This only affected the fallback used when a frame's source is not embedded in the source map, for example with `nosources-*` devtools, and now matches the Rspack compiler.

packages/repack/src/commands/webpack/Compiler.ts

@@ -276,7 +276,9 @@ export class Compiler implements CompilerInterface {
     }
 
     try {
-      const filePath = path.join(this.rootDir, filename);
+      const filePath = path.isAbsolute(filename)
+        ? filename
+        : path.join(this.rootDir, filename);
       const source = await fs.promises.readFile(filePath, 'utf8');
       return source;
     } catch {

packages/repack/src/commands/webpack/__tests__/Compiler.test.ts

@@ -1,8 +1,11 @@
 import type { EventEmitter } from 'node:events';
 import { Worker } from 'node:worker_threads';
+import { fs, vol } from 'memfs';
 import type { Reporter } from '../../../logging/types.js';
 import { Compiler } from '../Compiler.js';
 
+jest.mock('node:fs', () => jest.requireActual('memfs').fs);
+
 jest.mock('node:worker_threads', () => {
   const { EventEmitter } =
     jest.requireActual<typeof import('node:events')>('node:events');
@@ -70,3 +73,42 @@ test('terminates active workers when closed', async () => {
 
   expect(worker.terminate).toHaveBeenCalledTimes(1);
 });
+
+describe('getSource', () => {
+  const reporter: Reporter = {
+    process: jest.fn(),
+    flush: jest.fn(),
+    stop: jest.fn(),
+  };
+
+  const createCompiler = () =>
+    new Compiler(['ios'], { host: '' }, reporter, '/project', '/react-native');
+
+  beforeEach(() => {
+    vol.reset();
+  });
+
+  afterEach(() => {
+    jest.restoreAllMocks();
+  });
+
+  test('reads an absolute filename as-is', async () => {
+    vol.fromJSON({ '/outside/project/file.js': 'absolute source' });
+    const readFile = jest.spyOn(fs.promises, 'readFile');
+
+    await expect(
+      createCompiler().getSource('/outside/project/file.js', 'ios')
+    ).resolves.toBe('absolute source');
+    expect(readFile).toHaveBeenCalledWith('/outside/project/file.js', 'utf8');
+  });
+
+  test('resolves a relative filename against the project root', async () => {
+    vol.fromJSON({ '/project/src/index.js': 'source under the project root' });
+    const readFile = jest.spyOn(fs.promises, 'readFile');
+
+    await expect(
+      createCompiler().getSource('src/index.js', 'ios')
+    ).resolves.toBe('source under the project root');
+    expect(readFile).toHaveBeenCalledWith('/project/src/index.js', 'utf8');
+  });
+});